1. Field of the Invention
The invention relates to a data transmission method in a communication system, the system including at least one base station and at least one subscriber station, which subscriber station allocates capacity for connections. The invention also relates to a data transmission system, a base station and a subscriber station. The invention relates especially to packet transmission.
2. Description of the Background
Modem access systems support different higher layer protocols, which define the format and order of messages exchanged between two or more communication entities, as well as the actions taken on the transmission and/or reception of a message. The central task of the Medium Access Control (MAC) protocol is to allocate channel resources, typically radio channel resources. The MAC protocol defines how and when an access point or a subscriber unit may transmit on the channel. The MAC protocol includes required procedures for interfaces to provide guaranteed services to upper protocol layers.
In a centrally controlled access system, the access point is responsible for allocating capacity to subscriber stations on the uplink channel, i.e. for deciding when and for how long each subscriber station is allowed to transmit on the channel. The access point typically announces its scheduling decisions by transmitting control messages, sometimes called maps, which typically are broadcasted to all subscriber stations. These messages usually include a list of information elements, each one defining a capacity grant, specified i.e. by a starting time and a time frame for a transmission, addressed to a specific entity defined by the protocol.
For the end user the most important thing in communication networks is naturally that he can be satisfied with the end-to-end services he uses. An end-to-end service sets requirements regarding the Quality of Service (QoS). The requirements are mapped to the protocol hierarchy levels. For enabling a mapping between different hierarchy levels, the QoS requirements are usually classified.
The QoS requirements have to be fulfilled connection-specific. However, in centrally controlled access systems capacity is typically granted subscriber station-specific. Additionally, it should be noted that in many cases, one subscriber station may have several connections simultaneously. These connections may originate from more than one user equipment, and they have a defined QoS, which may be different for each connection. Thus there is a problem as to how the QoS requirements can be fulfilled for each connection.